The flexible polyurethane foams that are a part or the invention are well known in the industry. Information on preparation and common reactants can be found in many resources, including the Encyclopedia of Polymer Science and Engineering, Vol. 13, copyright 1988. John Wiley & Sons, Inc. Flexible polyurethane foams are used to make resilient structural materials such as cushioning or padding materials in the furniture and automotive industries. It is known to incorporate tire-retardant compounds into such foam materials to produce combustion modified flexible foam. However, care has to be taken so that adequate fire retardancy can be achieved without adversely affecting the desired physical properties of such foam materials. Increasing concerns over volatile organic compound emission levels and odor have resulted in a desire for incorporating polymeric or reactive flame retardant compounds into flexible polyurethane foam instead of additive flame retardant compounds.
Polyurethane foam is formed by a reaction between a polyol and diisocyanate. This reaction is highly exothermic.
Recently there has been an industry trend to move to lower density polyurethane foam. One result of this trend is that as the density of the foam decreases, the exotherm generated during the preparation of the foam increases, due to the high concentration of water needed to lower the density. Specifically it is the reaction of TDI and water that generates the largest exotherm during the polyurethane reaction.
One method that has been used to reduce this large exotherm is to use an auxiliary-blowing agent such as hydrofluorocarbons, low molecular weight hydrocarbons, or carbon dioxide. The addition of the auxiliary blowing agent reduces the amount of water needed to achieve the desired density and due to the lower amount of water, the exotherm is reduced.
Many auxiliary blowing agents that have been used in the past such as freons (chlorofluorocarbons), hydrochlorofluorocarbons and methylene chloride have come under attack recently for environmental reasons. The loam industry has since sought to prepare low density foams without the use of auxiliary blowing agents.
In addition, the manufacture of combustion modified flexible foams normally involves the production of large billets or buns of foam, which are set aside to cure or to complete the polymerization reaction. Temperatures within the billet from the reaction can reach 150 to 180° C. and higher. The insulating properties of the foam maintain this temperature in the interior of the billet for an extended period of time. Thus, components which are introduced into the foam, including the flame retardant components, should, if possible, be able to withstand high temperatures and not cause scorching or charring to be visible in the foam.
A common occurrence with introducing reactive flame retardants (≧97% reactive) into standard formulations for combustion modified flexible slabstock polyurethane foam is inconsistent air permeation throughout the polymer matrix. Uniform air permeation in combustion modified flexible slabstock polyurethane foam billets is an extremely important property. Air permeation has a direct effect on foam burn results, as well as, scorch prevention. Air permeation in combustion modified flexible slabstock foam having densities ranging from 1 pcf (pound per cubic foot) through 2.5 pcf will normally maintain a uniform air permeation result between 3 random samples within the same billet. Uniform air permeation results could be characterized as not having a maximum difference of <0.5 scfm (standard cubic feet per minute). Inconsistent air permeation outside of this range has the potential to cause flammability failures within the same foam bun or lower yields and higher foam waste due to scorch.
Additionally, combustion modified flexible slabstock polyurethane foam buns commonly exhibit discoloration and/or scorch in the center of the bun due to the high heat of reaction that forms the urethane linkages. The heat of reaction can degrade residual chemicals within the polymer matrix to form color bodies. Some of those residual chemicals, such as halogenated flame retardants produce halogenated acids that breakdown the urethane linkages, especially in the center of the bun. Although exothermic heat formation is taking place within the entire polymer matrix, the center of the bun experiences the highest temperature gradient because the surrounding polyurethane foam acts as a thermal insulation barrier, retarding heat dissipation.
There is therefore significant interest in developing new reactive flame retardant blends for combustion modified flexible polyurethane foams that prevent or minimize the effects of scorch and discoloration; as well as, maintaining uniform air permeation.
For example, U.S. Pat. No. 7,153,901, incorporated herein by reference in its entirety, discloses a liquid flame retardant; additive composition which comprises a liquid mixture formed from a) at least one reaction product of a brominated aromatic diester diol and an alcohol-reactive agent; b) at least one hindered amine antioxidant; and c) at least one phenolic antioxidant in which the phenolic ring is substituted by an alkanoic acid alkyl ester group in which alkanoic acid moiety has in the range of 2 to about 4 carbon atoms and the alkyl group has in the range of about 6 to about 16 carbon atoms; wherein (1) the proportions of a) to b) are in the range of about 30:70 to about 70:30; (2) the proportions of b) to c) are in the range of about 3:1 to about 1:3; and (3) the weight ratio of a) to b) plus c) is in the range of about 5:1 to about 25:1.
U.S. Published Patent Application No. 2009/0143494 discloses flame retardant additive for polyurethanes formed from (A) at least one bis(alkanoic acid ester) of a ring-brominated aromatic diester diol; (B) liquid alkylated triphenyl phosphate having an approximate average formula (RxPhO)3P═O) in which each R is, independently, a hydrogen atom or a C14 alkyl group and x is an average number in the range of about 0.2 to 3; and (C) at least one, alicyclic phosphonate ester having 1, 2 or 3 phosphorus atoms in the molecule, at least one of which is part of an alicyclic ring system, and having a phosphorus content of at least about 15 wt %.
U.S. Published Patent Application No. 2004/0171709; incorporated herein by reference in its entirety, discloses a flexible, flame-retarded, polyurethane foam comprising brominated and/or phosphorous flame retardants and an acid scavenger selected from hydroxides, carbonates, bicarbonates, amines, zeolites, hydrotalcites and epoxides. However, the application fails to disclose or suggest a mixture of at least one brominated aromatic diester diol and an epoxy resin.
European Patent Application No. 0 270 094 discloses flame retardant thermoplastic polyurethane compositions containing a halogen flame retardant containing 0.2 to 20 parts by weight of a cycloparaffinic compound having an epoxy group.
U.S. Provisional Patent Application No. 61/292,988, filed Jan. 7, 2010, incorporated by reference herein in its entirety, discloses a process for producing a tetrabromophthalic diester composition, a liquid reaction mixture is prepared comprising tetrabromophthalic anhydride (TBPA), a C2 to C6 polyhydric aliphatic alcohol (PAA) and an alkylene oxide (AO) selected from the group consisting of ethylene oxide and propylene oxide, said reaction mixture being substantially free of an organic solvent. While agitating the reaction mixture, the temperature of the reaction mixture is raised to at least 50° C. to allow the TBPA to react with the PAA and AO to produce a diester composition. The reaction is terminated when the diester composition has an acid value equal to or less than 0.25 mg KOH/gin of the diester composition.
According to the present invention, a novel reactive flame retardant blend has now been developed that maintains uniform air permeation, minimizes scorch and discoloration, as well as imparting flame retardancy, to combustion modified flexible polyurethane foams. The novel blend is a mixture of at least one brominated aromatic diester diol, an epoxy resin and optionally at least one hindered phenolic anti-oxidant.